1. Technical Field
The present invention relates to a method of forming a dielectric layer, and more particularly, to a method of forming a dielectric layer using a plasma enhanced atomic layer deposition technique.
2. Discussion of the Related Art
With the continued progression toward higher integration of semiconductor devices, a gate dielectric layer and a capacitor dielectric layer are required to exhibit the qualities of low leakage current and high capacitance within a limited area in transistor and capacitor devices. In this regard, the gate dielectric layer and the capacitor dielectric layer are preferably formed of high-k dielectric layers.
For depositing the dielectric layers, a sputtering method as such as physical vapor deposition method, or a chemical vapor deposition (CVD) method, are commonly employed. However, the sputtering method provides poor step coverage in regions where a step height difference is present. The CVD method offers the advantage of suitable step coverage and a high production yield, but also has the disadvantage of requiring a high temperature for forming a thin film. The CVD method is further limited in ability to precisely control the resulting thickness of the thin film to the degree of accuracy required, which, in highly integrated semiconductor devices, can be on the order of several
Recently, an atomic layer deposition (ALD) technique has been introduced to address the limitation of the CVD method and to form a thin film having a fine thickness according to the unit of an atomic layer.
The ALD method is characterized in that several thin films of atomic layers are alternately deposited by injecting each reactant material by a gas pulsing type to chemically deposit the reactant material on a substrate surface, and repeating the operation cycle several times. Particularly, the ALD method has been recently employed to meet the demands for forming a thin film with a high aspect ratio, with a high surface uniformity even in situations where the surface is relatively uneven, and with excellent electrical and physical properties. The gas pulsing type is a method of alternately supplying a reactant gas and a purge gas. Thin film formation using ALD offers advantages in that a deposited thin film has little residual material, and thickness control is relatively easy and reliable even in the case of thin film deposition with a thickness of 200 or less.
However, in the case where the thin film formation method using the ALD technique employs precursors having a high reactivity, it is difficult to secure reproducibility and reliability in the deposition process because the chemical and thermal stabilities of precursors can deteriorate. Further, removal of the precursors having high reactivity by a purging process can be a time-consuming process because it takes quite long to purge the reactant material adsorbed inside the chamber, thereby decreasing deposition speed and deteriorating fabrication productivity. Furthermore, in the case of using a reactant gas having a low reactivity, yet is stable chemically and thermally, increased deposition temperature is needed in order to activate surface reaction because of the low reactivity.
Among the efforts to overcome the decrease in productivity due to a decreased deposition speed in the thin film formation method using the ALD technique, a new method referred to as plasma enhanced atomic layer deposition (PEALD) has been recently introduced.
In the PEALD method, a first reactant gas is injected into a reaction chamber to adsorb the gas on a wafer surface, and a purge gas is supplied to remove the residual first reactant gas out of the reaction chamber. Then, a second reactant gas, which is excited by a plasma generator, is supplied into the reaction chamber. A method of forming a dielectric layer using the PEALD technique is disclosed in U.S. Pat. No. 6,486,047 in the title of “Apparatus for forming strontium-tantalum-oxide thin film”, the contents of which are incorporated herein by reference.
In the disclosure of U.S. Pat. No. 6,486,047, a strontium tantalum thin film is formed. In particular, a substrate is disposed inside a reaction chamber and heated. A source gas including strontium tantalum ethoxide is supplied into the reaction chamber along with a carrier gas. The vaporized source gas in the carrier gas is drawn out of the reaction chamber by a purge gas. An oxygen gas is supplied into the reaction chamber and becomes plasma. The oxygen plasma is drawn out of the reaction chamber by a purge gas.
However, the method disclosed in U.S. Pat. No. 6,486,047 is limited only to the source gas including strontium tantalum ethoxide, and cannot prevent the leakage current deterioration that commonly associated with an increase in device aspect ratio.
In the conventional formation method of a dielectric layer, leakage current characteristics are generally poor in a one-cylinder storage (OCS) cell capacitor having an aspect ratio of 7:1 or higher, but step coverage characteristics is improved by 85%. It is generally regarded that the deterioration of a leakage current results from the increase of impurities such as carbon within the layers due to the lack of oxygen radicals in the structure holes, not from the decrease of layer thickness, that is, a problem of step coverage characteristics. However, the increase of RF power to increase the amount of oxygen radicals may cause plasma damage to the device, and can cause a haze phenomenon at the edge portions of a wafer.
Therefore, a layer formation method technique that is capable of providing excellent electrical characteristics for preventing leakage current deterioration as well as a high deposition speed and suitable step coverage is desired.